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The present invention generally related to MPEG video decoders and, more particularly, to a system and corresponding algorithm for adjusting the,brightness and color information of MPEG encoded video images.
In the Motion Pictures Experts Group (MPEG) video standard, a sequence is comprised of a series of video frames. Each video frame in the sequence is subdivided into a number of rectangular information blocks, each containing a pixel, portion of the image. These information blocks are referred to as macroblocks. The pixel portions of the image are represented by a series of bits of data. In the MPEG video, standard, the data bits are encoded in a particular fashion. With respect to the attributes of the encoded image, the data bits contain information relating to the brightness (luminance) and color (chrominance) of the encoded image.
An MPEG decoder is used to decode the information present in each of the macroblocks to provide an image on a suitable display device. In the MPEG decoding methodology, motion compensation is performed on the image frames to adjust the image for any motion relative to the previous or subsequent reference frames. When the motion compensation stage is not a separate module within the MPEG decoder; the brightness and color controls are adjusted after the motion compensation and before display. To adjust the brightness and color, conventional decoders need to adjust all the pixel values comprising the image, which is a time consuming task. If a separate module performs the motion compensation, conventional decoders provide no means for controlling brightness and color.
The aforementioned and related drawbacks associated with known MPEG decoding schemes are substantially reduced or eliminated by the present invention. The present invention is directed to a system and corresponding method for adjusting the brightness and color of MPEG encoded video images. The disclosed system is a digital versatile disk player capable of decoding a previously encoded MPEG video signal and adjusting the brightness and color of the entire previously encoded MPEG video signal based on a subset of information contained in the encoded input signal. The disclosed system is capable of performing the brightness and color adjustment while the encoded MPEG video signal is in the frequency (dct) domain before motion compensation is performed. The digital versatile disk player of the present invention also includes means for determining whether the particular block to be decoded is of a predetermined type and decoding such block accordingly.
The present invention is embodied within a larger video display system comprising means for providing an input video signal having a plurality of encoded frames comprised of encoded macroblocks; decoding means for providing a plurality of decoded macroblocks comprised of decoded blocks, the decoding means including means for adjusting the brightness of the image represented by the encoded blocks contained within each macroblock in response to a first subset of data present in the, plurality of encoded blocks; and means for providing an output video signal in response to the plurality of decoded macroblocks, wherein the output signal is formatted to be displayed as a conventional video image. In a preferred embodiment of the present invention, the decoding means further includes means for adjusting the color of the image represented by the encoded macroblocks in response to a second subset of data present in the plurality of encoded blocks.
In a preferred embodiment of the present invention, the color and brightness properties of a decoded image in the frequency (dct) domain are adjusted by detecting whether the immediate macroblock is an intra block; extracting the luminance and chrominance blocks from the intra block; and adjusting the DC pixel component in the frequency domain, of each of the luminance blocks, wherein the brightness property of the image blocks is adjusted. For the chrominance blocks within the intra block, adjusting the DC pixel component in the frequency domain adjusts the color property of the image block.
An advantage of the present invention is that it provides the ability to independently control the brightness and color properties of decoded images when the last segments of decoding, e.g. IDCT (inverse discrete cosine transform) and/or motion compensation, are performed in a separate module.
Another advantage of the present invention is that it enhances the performance of MPEG video decoder devices.